Method for electrolytic production of hypobromite for use as a biocide

ABSTRACT

An electrolytic cell is provided that can include: a first electrode plate including a first surface that can include a graphite material; a second electrode plate including a second surface that can include a graphite material opposing the first surface; an electrolytic reaction zone between the first surface and the second surface; and an inlet to and an outlet from the electrolytic reaction zone. The first electrode plate and the second electrode plate can include impregnated graphite. The first electrode plate and the second electrode plate can essentially form a chamber for the electrolytic reaction. Methods are provided for using the electrolytic cells, a sodium chloride solution, and a sodium bromide solution, for on-site electrolytic production of hypobromite solution for use as a biocide in water systems.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patent application Ser. No. 10/448,793 filed May 30, 2003, that claims benefit under 35 U.S.C. § 119(e) from earlier filed U.S. Provisional Application No. 60/385,269, filed Jun. 4, 2002, both of which are herein incorporated by reference in their entireties.

FIELD

The present teachings relate to an electrolytic cell, methods for electrolytic production of hypobromite ion, and the production of biocides for industrial cooling systems using an electrolytic cell.

BACKGROUND

In many industrial and commercial processes excess heat can be generated, and the heat can typically be removed from the process by means of cooling water. Comfort cooling of living and work spaces can generate excess heat that can be removed from the air conditioning equipment by means of cooling water. The term “cooling water” is thus utilized to describe water that flows through equipment to absorb and remove heat. Equipment can include, for example, air conditioning units, engine jackets, refrigeration systems, and industrial heat exchangers. Equipment can be found in, for example, in the glass, automotive, chemical, steel, and petroleum industries; as well as commercial properties.

Water, due to its low cost and physical properties, can be a suitable material for transfer of heat and use as an evaporative cooler. Unfortunately, warm water, with dissolved and suspended solids, can be a medium for growth of microorganisms. An uncontrolled growth of microorganisms in re-circulating cooling water systems can create several severe problems, for example, increased risk of Legionnaires' disease; plugging due to physical blockage of cooling water passages; accelerated corrosion under biological masses; and/or reduced heat exchanger efficiency due to bio-fouling of surfaces.

These problems can be amplified by an increased desire in various industries to minimize water usage and wastewater discharge via increasing the concentration (cycles) at which cooling towers are operated, and the use of reclaimed wastewater as cooling tower makeup water. The solids and nutrient content of the cooling water can increase when a cooling tower is operated at higher cycles and/or with reclaimed wastewater as makeup. This makes the cooling water environment even more conducive to microbiological growth.

Current microbial fouling control programs rely upon various oxidizing and non-oxidizing biocides, that while often effective, can have numerous problems, for example, high costs, severe health and safety concerns, low efficiency, and incompatibility with other chemical products needed to operate at higher cycles.

Oxidizing biocides, such as chlorine, ozone, and chlorine dioxide, while cost effective at low dosages, can have the following disadvantages or a combination thereof:

-   -   many oxidizers, such as chlorine, can be dangerous to handle;     -   most oxidizers can react with many of the common scale and         corrosion inhibitors used in cooling water treatments;     -   organic oxidizers, such as hydantoin and controlled reactivity         hypobromite, can be costly;     -   many oxidizers, such as ozone, can be volatile, resulting in         higher usage and potential air pollution problems;     -   chlorine based oxidizers can have unwanted reactions with         various organics, causing potential discharge problems.

In addition to these problems, chlorine based products can lose much of their effectiveness as the water pH increases. The increasing popularity of alkaline water treatment programs, commonly operated at pH levels about 8.0 su, can thus make chlorine based products unusable for biological control.

Non-oxidizing biocides, such as dithiocarbamate, isothiazolin, and glutaraldehyde; while avoiding some of the problems related to oxidizers, can have the following problems during application. Recent research has shown that non-oxidizers can be ineffective against the Legionnaires' disease bacterium. Non-oxidizers can be very high use cost products, some, such as isothiazolin, are very dangerous to handle. Many non-oxidizers can have very slow reaction times, making them impractical to use in short half-life systems. Due to development of resistant organism populations, non-oxidizers can lose effectiveness and may need to be rotated. Further, some non-oxidizers can be highly regulated due to potential environmental problems.

SUMMARY

According to various embodiments, an electrolytic cell can be provided that includes a first electrode plate including a first surface that can be a graphite material; a second electrode plate including a second surface that can be a graphite material opposing the first surface; an electrolytic reaction zone including an electrolytic zone surface area between the first surface and the opposing second surface; an inlet to the electrolytic reaction zone; and an outlet from the electrolytic reaction zone. The electrolytic reaction zone can be a closed-cell such that all fluid flowing through the electrolytic cell flows along a flow path through the inlet, through the electrolytic zone, and through the outlet. An electrolytic solution stream can flow along a flow path from the inlet to the outlet and through the electrolytic reaction zone at a desired flow rate and can be capable of directing an entire cross-section of the electrolytic solution stream to completely flow between the opposing first and second surfaces. The first electrode plate and the second electrode plate can include impregnated graphite. The first electrode plate and the second electrode plate can essentially form a chamber for the electrolytic reaction.

According to various embodiments, a method of electrolytic production of hypobromite is also provided. The method can include providing an electrolytic cell; providing an electrolytic solution stream that includes sodium bromide, sodium chloride, and at least one of an aqueous solution, an aqueous mixture, water, or a combination thereof, and providing power to the first electrode plate and the second electrode plate. The electrolytic cell used for the method can include: a first electrode plate including a first surface; a second electrode plate including a second surface opposing the first surface; an electrolytic reaction zone including an electrolytic zone area between the first surface and the opposing second surface; an inlet to the electrolytic reaction zone; and an outlet from the electrolytic reaction zone. The electrolytic zone used for the method can be a closed-cell zone such that all fluid that flows into the inlet through the electrolytic reaction zone and through the outlet. The electrolytic solution stream can be directed through an entire cross-section of the stream to completely flow between the opposing first and second surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teachings are described in more detail below and with reference to the exemplary embodiments shown in the attached drawings which are intended to illustrate, not limit, the present teachings:

FIG. 1 is a perspective view of an electrolytic cell;

FIG. 2 is a top view of an electrolytic cell;

FIG. 3 is a side cross-sectional view of the electrolytic cell of FIG. 2; and

FIG. 4 is a process flow diagram of an electrolytic hypobromite generator.

DESCRIPTION OF THE VARIOUS EMBODIEMENTS

With reference to the drawings, according to various embodiments an electrolytic cell is depicted in FIG. 1 which is a perspective view of an electrolytic cell 100. A first electrode plate 102 and a second electrode plate 104 can be separated, sandwiched, and/or spaced-apart by an insulating and/or non-conducting spacer 110. An electrical power supply 108 can provide electrical power to the first electrode plate 102 and the second electrode plate 104. The first electrode plate 102, insulating spacer 110, and the second electrode plate 104 can define a chamber and/or an electrolytic reaction zone 114. The insulating spacer 110 can be present along the periphery of the first electrode plate 102 and the second electrode plate 104, for example, as a gasket. An inlet 106 and an outlet 112 can be used to provide a flow of a fluid and/or an electrolytic solution through the chamber 114 in the electrolytic cell 100. The direction of the flow is depicted by the unmarked arrows proximate to the inlet 106 and the outlet 112 in FIG. 1. Partial cut-away views of the first electrode plate 102, the second electrode plate 104, and the insulating spacer 110 can be seen in FIG. 1. The interior chamber 114 can be seen in both the partial cut-outs. The first electrode plate 102 and the second electrode plate 104 can include a graphite material impregnated with one or more resins impervious to water diffusion. The first electrode plate 102 and the second electrode plate 104 can be chemically resistant to the products of electrolysis.

According to various embodiments, the first electrode plate and the second electrode plate can include a graphite material, for example, an electrolytic grade graphite. Electrolytic graphite can be pure graphite produced by conversion of carbon to graphite. Electrolytic graphite can be produced in an electric furnace. The graphite can be electrolytic grade graphite that can be vacuum and pressure impregnated with a resin, for example, a hardenable resin to form impregnated electrolytic grade graphite. The graphite plates can also be manufactured by combining powered electrolytic grade graphite with various thermoset or thermoplastic plastic, resin powder(s). The graphite plates can be molded into an electrode in a heated press by means of filling a mold with the mixed powders and then compressing them with sufficient heat to fusion the resin(s) present. The impregnated or molded, electrolytic grade graphite can be impervious to water diffusion at pressures of, for example, at least about 100 pounds per square inch (PSI). The first electrode plate can include a first surface and the second electrode plate can include a second surface that faces the first surface. The electrode plates can include any one or more of a myriad of shapes, for example, they can be rectangular, circular, square, oval, elliptical, triangular, semicircular, rod-shaped, or any combination thereof. The two opposing electrode surfaces defining the electrolytic reaction zone 114 can include a graphite or graphite material surface. The two opposing surfaces defining the electrolytic reaction zone 114 can include a mixed metal oxide impregnation, or metal material layer that exhibits a low reactivity to the electrolytic solutions. A mixed metal oxide impregnation can give the graphite plates an additional low reactivity to the electrolytic solutions employed during operation of the electrolytic cell. The graphite material can be impregnated with a resin impregnation, a metal oxide impregnation, or a combination thereof.

According to various embodiments, the electrodes in an electrolytic cell can include graphite material impregnated with a hardenable resin, for example, an epoxy resin. The resin can be a phenol-formaldehyde resin, a phenol-furfural resin, a bisphenol epoxy resin, a halogenated bisphenol epoxy resin, a peracteic acid oxidized polyolefin epoxy resin, a methyacrylate resin, an acrylate resin, or any combination thereof. Electrodes manufactured by pressing can use much the same resins in a powdered form. The resins can include, but not be limited to, such resin materials as polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyvinylidene fluoride. Mixed metal oxides, such as manganese-iron oxides, can be incorporated into the electrodes prior to impregnation by diffusion of appropriate water soluble salts, followed by heating, or mixed directly into the powders prior to pressing of the electrodes when the press method of manufacture is used.

According to various embodiments, an insulating spacer can be disposed between the first surface and the second surface. The first surface can have an outer periphery and the insulating spacer can be flat and include an outer peripheral edge that has a shape that corresponds to the shape of the outer periphery of the first surface. The space bound by the first surface, the spacer, and the opposing second surface when constructed together can define an interior chamber defining, at least in part, an electrolytic reaction zone. The insulating spacer can act as a gasket and spacer for the chamber defined between the two electrode plates. The insulating spacer can be electrically insulating. The insulating spacer can be chemically inert. The insulating spacer can include a material selected from neoprene, fluoroelastomer, vinyl, silicone rubber, a low density polyethylene, or a combination thereof VITON™ available from Dupont Dow Elastomers of Wilmington, Del. is an example of a fluoroelastomer that can be used as an insulating spacer. The insulating spacer can have a thickness of less than or equal to about one inch, for example, about 0.5 inches, about 0.3 inches, or about 0.25 inches. The insulating spacer can be made without any fabric reinforcement in its composition. The insulating spacer can have an outer periphery larger, smaller, or equal to an outer periphery of the first and/or the second electrode. The insulating spacer can have an inner periphery that is smaller than the smallest outer periphery of the two electrodes.

According to various embodiments, the inlet can be a hole through the first electrode plate, the second electrode plate, or the insulating spacer. The outlet can be a hole through the first electrode plate, the second electrode plate, or the insulating spacer. The inlet hole and the outlet hole can be positioned on opposite sides and opposite corners of the electrolytic reaction zone.

According to various embodiments, a power supply can be electrically connected to the first electrode plate, the second electrode plate, or both plates, of an electrolytic cell. The power supply can be a battery, a direct current (DC) power supply, or an alternating current (AC) power supply. The power supply can be a switchable power supply. The power supply can be used to provide the desired DC to the electrodes. The power supply can be a rectifier power supply operating from typical commercial AC power.

According to various embodiments, the power supply can be capable of maintaining a constant, set current to the electrolytic cell. For example, the power supply can be capable of providing a direct current of from about 0.25 amps per square inch of electrolytic zone electrode surface area (amps/in²) to 1.5 amps/in², at a voltage of from about one Volt DC to about 24 Volts DC. The voltage can be, for example, from about two Volts DC to about 12 Volts DC, or from about 2.5 Volts DC to about 10 Volts DC, or from about four Volts DC to about eight Volts DC. The power supply can be capable of supplying about one amp hour of power per each molar portion of sodium bromide, sodium chloride, and water, needed to produce from about 1.0 gram to about 1.1 grams of hypobromite measured as chlorine. The power supply can be capable of reversing a polarity of a current supplied to the first electrode plate and the second electrode plate on a cycle of from about one minute to about 1440 minutes per cycle.

According to various embodiments, the cross-section of an electrolytic solution stream flowing through the electrolytic reaction zone can be rectangular in shape, square in shape, oval or elliptical in shape, for example. The electrolytic zone electrode surface area can be the combined surface area of the first surface of the first electrode plate and the second surface area of the second electrode plate, for example, to the extent those surfaces can contact an electrolytic solution flowing through the electrolytic reaction zone. The electrolytic reaction zone electrode surface area can be the sum of the first electrode surface area and the opposing second electrode surface area to the extent those surface areas are not in contact with the insulating spacer

According to various embodiments, the electrolytic solution system can include a positive displacement pump. The pump can have an adjustable flow rate, for example, via a variation in a pump stroke, via a variation in a speed.

The electrolytic solution system can include a pressurized water supply wherein the pressurized water supply is capable of maintaining a constant, set-flow of pressurized water supply. The pressurized water supply can include a pressure regulator, a flow regulator, and a water supply. The electrolytic solution system can include an in-line mixer. The electrolytic solution system can include a mixture supply system including a mixture supply outlet. The electrolytic solution system can maintain a pressure internal to the electrolytic reaction zone. A flow rate can be maintained by the electrolytic solution system at a pressure that can be, for example, a rate of up to about 100 PSI, for example, up to about 25 PSI, up to about 50 PSI, up to about 75 PSI, up to about 100 PSI, or up to about 200 PSI or greater.

In an exemplary system, the electrolytic solution system can include a pump, a mixture system with a mixture supply outlet, a pressurized dilution water supply including a pressurized water supply outlet, a water supply, an in-line static mixer to combine the supply from the mixture supply outlet, the pressurized water supply outlet, or a combination thereof. The electrolytic solution system can form a diluted electrolytic solution.

According to various embodiments, the mixture system can include a first pump having a first pump outlet in fluid communication with a supply that can include a sodium bromide solution, for example, a 40% by weight aqueous solution of sodium bromide in water referenced as PCT 3038, also available from ProChemTech International, Inc., Brockway, Pa., and a second pump having a second pump outlet in fluid communication with a supply that can include a sodium chloride solution, for example, 22.7% by weight aqueous solution of sodium chloride in water referenced as PCT 3039, also available from ProChemTech International, Inc.

The mixture supply system can provide a supply of sodium bromide that can include, for example, from about 35% by weight to about 45% by weight sodium bromide solution, and a supply of sodium chloride solution that can include, for example, from about 20% by weight to about 25% by weight sodium chloride solution. The mixture supply system can provide a supply with a mixture ratio of the sodium bromide solution and the sodium chloride solution, to the metered water supply of from about 1:10 to about 1:30. The mixture system can include a single solution supply system with an appropriate mixture ratio of sodium chloride and sodium bromide, such as PCT 3024, an aqueous solution of 22.3% sodium bromide and 12.7% sodium chloride in water, also available from ProChemTech International, Inc. The mixture system can provide any solution capable of an electrolytic reaction using any number of solution supplies.

According to various embodiments, an electrolytic cell can include at least two electrodes. The electrolytic cell can include two electrodes, with a first electrode capable of performing as an anode and the other of two electrodes performing as a cathode. The electrolytic cell can include more than two electrodes, with the first electrode capable of operating as an anode, the second electrode capable of operating as a cathode, and any and all additional electrodes acting as bi-polar electrodes.

FIG. 2 is a top view of an exemplary embodiment of an electrolytic cell 120. The electrolytic cell 120 can include a first electrode plate 122, an insulating spacer 130 (shown in phantom), and a second electrode plate (not shown) joined together using a first set of bolts 138 to sandwich the insulating spacer between the first electrode plate 122 and the second electrode plate. The first set of bolts 138 can be electrically insulating. The first set of bolts 138 can include nylon bolts, plastic bolts, metal bolts used with insulating sleeves and washers, metal bolts insulated using rubber, or a combination thereof. Nylon, other plastic, or metal nuts can be used. The first set of bolts 138 can be chemically inert. Buss bar 134 can be connected to the first electrode plate 122 using a second set of bolts 136. A second buss bar (not shown) can be connected to the second electrode plate. Buss bar 134 and the second buss bar can be used to provide electrical power to electrolytic cell 120. The buss bar 134 can include an electrically conductive metal and the second set of bolts 136 can be electrically conductive, for example, made of stainless steel, copper, iron, or the like. An inlet 126 can be disposed in the first electrode plate 122 and an outlet 132 (shown in phantom) can be disposed in the second electrode plate. The inlet 126 and outlet 132 can includes extensions threaded to or otherwise connected to the first electrode plate and the second electrode plate, respectively. The electrode plates can each have two opposite, parallel, planar sides, or parallel, or planar surfaces. A hole 142 can be provided to connect the cell 120 to a power supply (not shown). The hole 142 can be threaded.

FIG. 3 is a side cross-sectional view of the electrolytic cell 120 taken along line 3-3 of FIG. 2. Depicted in FIG. 3 is an insulating spacer 130 that in-part defines the electrolytic reaction chamber 140 for an electrolytic solution or fluid flowing through the electrolytic cell 120. A first unmarked arrow in chamber 140 and a second unmarked arrow in the outlet 132 depict the direction of the electrolytic solution flow. The second electrode plate 124 is visible in FIG. 3. The cross-sections of the first set of bolts 138 are depicted in FIG. 3. The cross-sections of the second set of bolts 136 can be seen in FIG. 3. A first surface 146 and a second surface 144 can at least in-part define an electrolytic reaction zone electrode surface area. The inlet is not shown in FIG. 3. The first electrode 122, buss bar 134, and threaded hole 142 are also depicted in FIG. 3.

The scale of various parts of the apparatus depicted in FIGS. 1-3 does not necessarily represent required or desired dimensions of an electrolytic cell.

Electrolytic cells can be designed for outputs of from about 0.25 lbs/day to about 500 lbs/day, for example, about one lb/day, about five lbs/day, about 10 lbs/day, about 20 lbs/day, about 100 lbs/day, or about 500 lbs/day of hypobromite measured as free chlorine. Exemplary design parameters for an electrolytic cell to produce 5 lbs/day of hypobromite measured as free chlorine can be:

-   -   Plate spacing—about 0.25 inches     -   Plate area—about 81 square inches     -   Operating voltage—about 9 to 10 VDC     -   Required amperage—about 86 Amps     -   Salt feedrates—about 0.24 gallons per hour (GPH)     -   Dilution water feedrate—about 6.3 GPH

The apparatus can include an electrolytic cell, a DC power supply, an in-line mixer for mixing electrolytes with dilution water, appropriate metering pumps for the electrolytes, a dilution water flow controller, and a system control panel.

FIG. 4 is a process flow diagram for an electrolytic hypobromite system 200. A pressurized source of water, such as water supply 202, can be controlled using a solenoid valve 204 in fluid communication with a pressure regulator 206 and a flow controller 208. A plurality of chemical pumps, shown in FIG. 4 as a first metering pump 210 and a second metering pump 214, can supply a plurality of chemicals needed for the electrolytic process. Sodium bromide solution 212 and sodium chloride solution 216, for example, can be fluidly connected to the first metering pump 210 and the second metering pump 214, respectively. Sodium bromide solution 212 and sodium chloride solution 216 can be mixed with water from the flow controller 208 using a solution union 218, for example, a T-junction. An in-line mixer 220 can be used to obtain a uniform mix of solutions downstream of the solution union 218. The uniform mix can be processed by an electrolytic cell 222. A control panel 224 can be used to control the first metering pump 210, the second metering pump 214, and a power supply 226. The power supply 226 can be electrically connected to the electrolytic cell 222. Fluid output from the electrolytic cell 222 can flow into a water well 228. The water well 228 can receive a hypobromite solution as shown in FIG. 4. The composition of the solution flowing from the electrolytic cell 222 to the water well 228 can be different if the sodium bromide solution 212 and the sodium chloride solution 216 are replaced by other chemicals. The water well 228 can be used with a gas separator (not shown) to vent a gas resulting from the electrolytic reaction, for example, Hydrogen gas (H₂). The water well 228 can be, for example, a cooling tower, a water supply system, a reservoir, or the like.

According to various embodiments, the method can include setting a flow rate of the electrolytic solution stream to obtain a conversion efficiency of bromide to hypobromite ion, of about 95% or greater. The flow rate of the stream can be set to control the cell to produce from about 0.5 gram to about 1.5 grams of hypobromite (measured as chlorine) for each amp hour of power provided.

According to various embodiments, the sodium bromide can include a sodium bromide solution, and the sodium chloride can include a sodium chloride solution. In an exemplary system, the sodium bromide solution can include from about 35% by weight to about 45% by weight sodium bromide, and the sodium chloride solution can include from about 20% by weight to about 25% by weight sodium chloride. The electrolytic solution can have a mixture ratio of the sodium bromide solution and the sodium chloride solution, to water, of from about 1:10 to about 1:30.

According to various embodiments, the electrolytic solution stream can be pumped to maintain a pressure of at least about 100 PSI in the electrolytic cell.

According to various embodiments, the electrolytic solution stream can include a sodium bromide and sodium chloride solution that can include from about 17.3% by weight to about 27.3% by weight sodium bromide, and from about 7.7% by weight to about 17.7% by weight sodium chloride, with the balance being water.

According to various embodiments, a system is provided that can include an electrolytic cell, a control panel, a power unit, two feed pumps, and an in-line mixer. An integral internal timer, possibly in the control panel, can control operation of the system for slug feed applications. The timer can be used to turn the system on and off. With this system, the hypobromite solution can be directly discharged into a cooling tower basin so as to vent off the hydrogen gas produced by the electrolytic cell.

According to various embodiments, a system is provided that can include an electrolytic cell, a control panel, a power unit, two feed pumps, an in-line mixer, a vented hypobromite storage tank with a level sensor, and a transfer pump drawing from the vented storage tank. An integral timer, in the control panel, can control operation of the transfer pump to discharge hypobromite solution on an on-off basis. The discharge can be into highly pressurized lines, into areas that do not provide appropriate venting for produced hydrogen gas. The discharge can be in greater slug dose amounts than can be provided by direct operation of the electrolytic cell, depending on treatment circumstances, by appropriate provisioning of such immediate amounts of hypobromite solution. Operation of the electrolytic cell can be automatically controlled by the level sensor in the vented tank. The level sensor can be utilized to maintain the vented tank in a “full” condition. Hydrogen gas produced by the electrolytic cell can be vented from the storage tank.

According to various embodiments, the system can include one or more of a Hach chlorine analyzer control, an Oxidation Reduction Potential (ORP) analyzer control, an electrolytic cell, a control panel, a power unit, two feed pumps, an in-line mixer, a vented hypobromite solution storage tank, a level sensor for the vented hypobromite solution storage tank, and a variable speed pump drawing from the vented tank. A hypobromite detector can be included, for example, a Hach chlorine analyzer, or an ORP analyzer. The detector can be capable of detecting hypobromite in a treated solution, such as cooling tower water, wherein the hypobromite detector can generate an output signal. The output signal can be utilized to vary the variable speed pump output in proportion to the signal received. The output signal can be utilized to maintain a preset or user-defined concentration of hypobromite in the water contacting the hypobromite detector. The vented hypobromite solution storage tank level sensor can control the operation of the electrolytic cell maintaining the tank in a “full” condition. Hydrogen gas in the storage tank can be vented.

According to various embodiments, the system and the various control systems therein can be utilized to maintain a hypobromite residual level as bromine in the treated water of from about 0.2 mg/l to about 5.0 mg/l. The hypobromite residual level can be measured one hour after a slug feed. The hypobromite residual level can be measured on a continuous basis. The hypobromite residual level can be measured for effective biocidal control. Dependent upon specific treated water variables, higher levels, such as 1.0 mg/l to 15.0 mg/l may be desired, or required, to be effective for biocidal control.

Any appropriate range DPD-based bromine or chlorine test kit can be used for control purposes using, for example, material testing. The conversion factor from chlorine to bromine is 2.25.

According to various embodiments, the method can include making two equimolar aqueous solutions of sodium bromide and sodium chloride, and feeding these solutions in exact portions, with sufficient dilution water, into an electrolytic apparatus. Within the electrolytic apparatus, application of a controlled voltage DC current can convert a bromide ion to a hypobromite ion at an efficiency that of about 95% or greater.

The teachings described herein can be based upon the following electrolysis reactions:

-   1. 4H₂O+4e-=4OH—+2H₂ -   2. 2Cl—=Cl₂+2e- -   3. 2OH—+Cl₂ 32 ClO—+Cl—+H₂O -   4. ClO—+Br—=BrO—+Cl— -   5. 2 Br—=Br₂+2e- -   6. 2OH—+Br₂=BrO—+Br— -   7. Cl— and Br—from the right hand side of reactions 3, 4, and 6 can     recycle back to reactions 2 and 5 respectively, to drive the     conversion to about 95% or greater efficiency as to the conversion     of Br— to BrO—. Reaction 4 can be a replacement reaction that goes     to completion without application of any electromotive force.

According to various embodiments, the method can be modified as desired for adjusting, for example, the amount of hypobromite (BrO—) in the outgoing solution, the molar balance of chloride to bromide ion in the salt solutions, the conductivity of the diluted salt solution, the relationship of voltage to electrode plate spacing, and the required amperage-time relationship.

According to various embodiments, methods are provided that include the processing of two equimolar solutions of sodium bromide and sodium chloride. The two solutions can be mixed together to generate 40% by weight sodium bromide and 22.7% by weight sodium chloride, dissolved in water. These solutions or mixed solution can then be fed at a controlled rate into the electrolytic apparatus with sufficient dilution water so as to obtain about a 1:27.7 dilution of the salt water. Within the electrolytic apparatus, application of DC current to such a solution can produce from about 1.0 gram to about 1.1 grams of hypobromite measured as free chlorine for each amp-hour of power applied. This can result in production of a hypobromite solution with a concentration, as free chlorine, of approximately 0.38%. A process flow diagram of the process is depicted in FIG. 4.

According to various embodiments, methods are provided that include the use of two electrodes and an insulating plate. According to various embodiments, the electrodes used can each include a titanium plate including a platinum coating having a thickness of from about 200 to about 300 mils ( 1/1000 of an inch, or about 0.2 inches to about 0.3 inches).

While specific materials are mentioned above, the construction of the electrolytic cell electrodes can include resin-containing graphite, titanium electrodes plated with 200 to 300 mils of platinum, or the like. The methods can include the use of any these electrode types and can be modified as desired by adjustments to one or more of: the spacing of the plates; the plate area; the voltage and amperage of the power supply; and the feed rates for the salt solutions and water.

The methods and apparatus taught herein can be used in large industrial and commercial cooling systems, for example, over 200 tons. The system can produce a solution of sodium hypobromite on demand that is very effective for control of algae, bacteria, and fungi in cooling systems.

In comparison to current technology, the methods, apparatus, and the hypobromite product produced according to the teachings herein can offer multiple specific advantages.

In the area of health and safety, the reagents can be pH neutral, inert, stable, salt water solutions that can be totally non-hazardous. For reactivity, the chemical reactivity of the freshly produced hypobromite can be very high, resulting in a quick kill of target organisms. The product can be produced “on demand” and has no problems with loss of activity in storage.

Hypobromite produced by the apparatus and methods taught herein can include a very low chlorine and hypochlorite content, in contrast to products such as hydantoin where 50% of the halogen content is chlorine. This property can make the produced hypobromite less aggressive to scale and corrosion inhibitors, and can make the hypobromite more compatible. Produced hypobromite can stay more active longer in a cooling tower.

The produced hypobromite can penetrate and remove biofilms better than chlorine based biocides. The hypobromite can be more effective at high pH values than chlorine based biocides. The produced hypobromite can be more cost effective than any non-oxidizing biocide and most competing oxidizers. The produced hypobromite reacts with fewer organics, and in smaller amounts, than chlorine based products, thus forming fewer and lesser amounts of undesirable byproducts, such as, AOX and THM, “halogenated organics.” Thus, the produced hypobromite can be more environment friendly.

Electrolytic cells constructed by the teachings in this disclosure can substantially reduce construction costs. The cost of resin or metal-oxide impregnated electrodes, either molded or pressed, can be substantially less than electrodes constructed of typical materials, such as platinum plated titanium. The use of the resin impregnated graphite permits construction of the electrolytic cell such that the electrodes can become the electrolytic solution container. This can substantially lower the cost of the electrolytic cell.

The present teachings relate to other embodiments of the methods and apparatus disclosed herein. Embodiments apparent to those skilled in the art from consideration of the present teachings and their practice of the present teachings are included herein. It is intended that the present specification and examples be considered as exemplary only with a true scope and spirit of the teachings being indicated by the following claims and equivalents thereof. 

1. A method of electrolytic production of hypobromite, the method comprising: providing an electrolytic cell, the cell comprising: a first electrode plate including a first surface; a second electrode plate including a second surface opposing the first surface; an electrolytic reaction zone between the first surface and the opposing second surface; an inlet to the electrolytic reaction zone; and an outlet from the electrolytic reaction zone; providing an electrolytic solution stream comprising sodium bromide, sodium chloride, and at least one of an aqueous solution, an aqueous mixture, water, or a combination thereof; providing power to the first electrode plate and the second electrode plate; and pumping the electrolytic solution stream along a flow path from the inlet to the outlet and through the electrolytic reaction zone, wherein the electrolytic reaction zone is a closed-cell such that all fluid flowing through the electrolytic cell flows along a flow path through the inlet, through the electrolytic reaction zone, and through the outlet.
 2. The method of claim 1, further comprising setting a flow rate of the stream to obtain a conversion efficiency of bromide to hypobromite ion of about 95% or greater.
 3. The method of claim 1, wherein the sodium bromide includes a sodium bromide solution from about 35% by weight to about 45% by weight sodium bromide, and the sodium chloride includes a sodium chloride solution comprises from about 20% by weight to about 25% by weight sodium chloride.
 4. The method of claim 1, wherein the electrolytic solution is a mixture having a mixture ratio of the sodium bromide and the sodium chloride, to water from about 1:10 to 1:30.
 5. The method of claim 1, further comprising setting a flow rate of the electrolytic solution stream to control the electrolytic cell to produce from about 0.5 grams to about 1.5 grams of hypobromite measured as chlorine for each amp hour of power provided.
 6. The method of claim 1, wherein at least one of the first and second surfaces comprises graphite.
 7. The method of claim 1, wherein the electrolytic cell further comprises an insulating spacer disposed between the first surface and the opposing second surface.
 8. The method of claim 1, wherein the insulating spacer has a thickness of less than or equal to about 0.25 inches.
 9. The method of claim 1, wherein the inlet is a hole through one of the first electrode plate and the second electrode plate, and the outlet is a hole through the other of the first electrode plate and the second electrode plate.
 10. The method of claim 1, wherein the electrolytic reaction zone includes an electrolytic zone electrode surface area, and wherein providing the power provides a current from about 0.5 amps per square inch to about 1.5 amps per square inch of electrolytic cell surface.
 11. The method of claim 1, wherein the providing power provides from about 0.5 amp hours to about 1.5 amp hours of power per square inch of electrolytic zone surface area per each molar portion of sodium bromide, sodium chloride, and water, needed, to produce from about 1.0 gram to about 1.1 grams of hypobromite measured as chlorine.
 12. The method of claim 1, wherein a polarity of the current supplied by the power is reversed to the first electrode plate and second electrode plate at a cycle of from about one cycle per 1 minute to about 1 cycle per 1440 minutes.
 13. The method of claim 1, wherein pumping the electrolytic solution stream maintains a pressure of at least about 100 PSI in the electrolytic cell.
 14. The apparatus of claim 1, wherein the electrolytic solution stream includes a sodium bromide and sodium chloride solution that includes from about 17.3% by weight to about 27.3% by weight sodium bromide, from about 7.7% by weight to about 17.7% by weight sodium chloride, and the balance being water. 